how would the sender know that IT had flagged their email as external before the email was sent and flagged? The recipients who fall for it don't think about t

how would the sender know that IT had flagged their email as external before the email was sent and flagged? The recipients who fall for it don't think about that. They think "oh crap, the big boss needs this done". Critical thinking about and questioning of decisions from higher up is strongly -- one might even say violently -- discouraged in many large organizations.